The pistons of internal combustion engines typically include a cylindrical base that has a bottom portion connected to a crank shaft by a connecting rod or the like, and a top portion or piston crown opposite the bottom portion. The piston crown cooperates with the cylinder head to define a combustion chamber. It is within the combustion chamber that air and fuel are mixed and ignited.
The piston crown is typically bowl-shaped and defined by a circumferential wall that extends from the cylindrical base of the piston. The circumferential wall of the piston may also be known as the piston bowl wall. A fuel injector is typically mounted in the cylinder head and extended into the combustion chamber to communicate fuel to the combustion chamber prior to ignition. Upon ignition, the resulting flame plumes flow radially outward and impinge against the piston bowl wall. When the flame plumes collide with the piston bowl wall, a stagnation point is created around the point where flame plumes hit the piston bowl wall. Such stagnation points cause the momentum of the flame plumes to be reduced.
While effective, such pistons within internal combustion engines, be they Otto or Diesel engines, have difficulties in reducing soot formation and increasing soot oxidation. More specifically, as soot results from incomplete combustion of hydrocarbons, pistons with traditional piston geometries may not have sufficient fuel-air mixing to avoid such incomplete combustion. Typical diesel combustion systems rely on fuel spray and combustion chamber interaction to mix fuel and air quickly for ignition and combustion. Ignition is caused by the compression of mainly air (which may typically include recirculated exhaust gas (EGR)) to a sufficient temperature and density through the piston compression stroke before fuel injection. A combustion chamber formed by a piston reciprocating within a cylinder closed by a cylinder head is typically utilized to help mix the fuel with the air to thereby reduce soot formation and increase soot oxidation. However, a problem associated with such traditional piston design is that flame plumes travelling from a fuel injector within the combustion chamber may interact and collide, thereby increasing the soot emissions. Accordingly, a problem that the piston design may try to avoid is to prevent flame plume interaction. If the piston can reduce the flame plume interaction, then soot oxidation may be increased, and the net soot formation, where the net soot formation is equal to the soot formation minus the soot oxidation, may decrease. However, reducing flame plume interaction may be harder and more costly under a traditional piston geometry for a piston located within a typical internal combustion engine.
Another problem with traditional piston design is that unused air and gas may flow in and out of the piston bowl without any interaction with the fuel-rich region of the combustion chamber. Although flame plumes are formed and travel within the piston bowl, the fuel spray and combustion chamber interaction may not be enough to prevent a significant amount of unused air and fuel from leaving the piston without mixing with the fuel-rich region and combusting. In other words, the geometry of the piston may have limitations in ensuring an efficient flow of air to mix with the fuel region in the piston bowl.
Pistons of the type generally described above are known in the art. For example, Japanese Patent No. JPH1122988 and entitled “Combustion Chamber of Direct Injection Diesel Engine,” discloses a method for promoting the mixture of air and spray fuel within a cavity by reducing the intake swirl and dispersing the spray fuel while utilizing the intake swirl and squish flow. In another example, U.S. Pat. No. 8,646,428 entitled “Piston Positioned for Reciprocal Movement in a Combustion Engine Cylinder,” discloses a piston positioned for reciprocal movement in a combustion engine cylinder wherein protrusions are arranged half way between flame plume impingement areas. However, improved combustion and reduced soot formation continue to be problematic in the field.
In view of the foregoing disadvantages with pistons with traditional geometries, a need exits for a solution which provides a more reliable and efficient way to increase the beneficial mixing of air and fuel within the piston bowl to thereby reduce flame plume interaction and increase soot oxidation. The present disclosure is directed at addressing one or more of the deficiencies and disadvantages set forth above. However, it should be appreciated that the solution of any particular problem is not a limitation on the scope of this disclosure or of the attached claims except to the extent expressly noted.